The people, mostly from the partnering Lincoln Park Zoo and Lake County Forest Preserve District, were scientists, public-relations specialists, photojournalists, even an intern, all of them, at times, watching the reptiles like hawks, though with the opposite intent of actual hawks.

The snakes had been at the zoo that morning, where they had been "head-started" — grown quickly to adult size over the previous year — and then placed into pillowcases and into a cooler, driven north in a zoo minivan, then marched into the middle of this central Lake County field, well away from roadway or hiking trail.

The new home was perfect, said Allison Sacerdote, the Lincoln Park Zoo reintroduction biologist who is coordinating the Smooth Green Snake Conservation Partnership (and who is believed by her colleagues to be the first person in the country, possibly the world, with the title "reintroduction biologist").

"It has all of the components you can think of," she said. "Old trees, downed wood, humidity …"

And as one after another of the snakes slid off of Sacerdote's and others' hands and into the temporary enclosures constructed to ease their return into the wild, another small victory was won in an ongoing battle.

This extraordinary effort over less than one pound of snake is being made because Lake County, under continual development as a Chicago exurb, has been coming up short in counts of some native species that ought to be there, such as this once widespread, harmless-to-humans reptile, biologically adapted to blend in with long grasses that once covered the prairie.

Smooth green snakes are officially endangered in Indiana and Iowa. Loss of habitat and pesticide use do them no favors. In Illinois, they are on a watch list labeled "In greatest need of conservation."

"Green snakes have been declining in Lake County in particular," said Gary Glowacki, a wildlife biologist with the Forest Preserve District who has been the point man on the Lake County side of the partnership. "They're a really important part of the ecosystem. They're both predator and prey. And they're an important part of the natural heritage of Lake County.

"We do have a few populations remaining, but they should be more widespread. Our goal is to restore the populations to the numbers they once were."

That's not going to happen with an 18-snake release, but this program, which also had a successful 18-snake release in 2011, is an experiment, funded in part by an anonymous grant in Lake County, in part by the zoo through its conservation mission.

Sacerdote delivered a talk on it, "Smooth Green Snake Recovery Efforts in Northern Illinois," to her zoology peers at the World Congress of Herpetology in Vancouver, British Columbia, in mid-August. She is working on a paper.

The scientific emphasis, she explained, is on how best to head-start the snakes, and on which is better: "hard release" (placing them directly into the natural environment) or "soft release" (using protective enclosures such as the ones in Lake County to keep out prey until the snakes have acclimated and establish "site fidelity").

"The Lincoln Park Zoo has done these throughout the world," Glowacki said. "It's nice to do it with a local example."

Other species the zoo has raised for reintroduction programs include ornate box turtles to help restore an old Army depot in Savanna, Ill., and red wolves to help repopulate the species in the Carolinas.

In Lake County, Sacerdote and Glowacki are also working to trap and monitor — and, perhaps, eventually breed and rerelease — the meadow jumping mouse and least weasel, two other native species in need of a jump-start. (And in July, Sacerdote said, the zoo won an Illinois Department of Natural Resources grant to begin monitoring smooth green snake populations in McHenry and DuPage counties.)

At the zoo, smooth green snakes occupy a terrarium environment in the main children's zoo building, flanked by river otters on one side, beavers on the other. Signage explains that the snakes on display are part of a project to restore the species to the wild.

"Get them hooked on a cute snake," added Glowacki. "People light up and seem to take a shine to green snakes. … They make a really good mascot for grassland conservation."

"It's a good mascot," said Sacerdote, "for snake conservation too."

Most of the green snakes were raised from the eggs of females captured while gravid — pregnant — but one snake did lay eggs after being in captivity a year, Sacerdote said. It's possible she may have been impregnated in the wild, however, as the snakes are capable of storing sperm.

"At the zoo, we are trying to get them to grow as quickly as possible," she said, explaining that the rate was probably two or three times what it would have been. "Being large gives them a better chance once they're out in the environment."

It'll be about a month before the enclosures in the field — roofing-tile walls dug into the ground, with a wire-fence perimeter and top, plus a small plastic dish to help accumulate moisture — are removed.

In the meantime, Sacerdote, who works mostly in Lake County, will check on the snakes, which have identification markings on their undersides, most mornings, a time when they tend to be more active than in the heat of the day. "They seem to be doing well," she reported Tuesday, a week after the release. "They have plenty of water. I was able to observe a couple while they were hunting crickets in the enclosure. Grasshoppers, as well."